Such a method is known example from DE 10 2007 015 876 A1.
Modern internal combustion engines are provided with a common rail injection system with which fuel is conveyed by a pump into a pressure reservoir (common rail) and is pressurized. The fuel is then injected from the common rail via controllable injectors into the combustion chambers of the internal combustion engine.
A common rail injection system is known for example from DE 198 34 660. The common rail is provided with a rail pressure sensor with which the pressure in the rail is measured, with a pressure valve and/or the pump of the injection system being controlled using open-loop and/or closed-loop control depending on the measured pressure. The (analog) pressure signal of the rail pressure sensor which is processed in the control device is thus the control variable for closed-loop control of the rail pressure. An error function of the rail pressure sensor or drift behavior during operation and over the lifetime of the rail pressure sensor respectively have a negative affect on the accuracy of the setpoint pressure to be set and thereby on the precision of the injection amount.
Component faults occurring in the common rail injection system frequently lead to undesired vehicle behavior in which the engine is only able to be started with difficulty or is no longer able to be started at all. On-board diagnosis systems only allow the precise cause of the error in the injection system to be determined to a restricted extent for starting problems, for example with an electrical short circuit, without any active intervention into the system. This also applies especially for a defective rail pressure sensor e.g. one exhibiting an offset, but free from electrical errors however. Typically it is then only possible to detect whether the rail pressure control is approaching a limit, without actually being able to fully distinguish whether a valve or the rail pressure sensor is now defective for example.
Because of this lack of knowledge of the precise cause of the error unnecessary components or too many components are frequently replaced. Thus the described undesired vehicle behavior can typically initially lead to the replacement of the high-pressure pump although the start problem is actually being caused by a drifted rail pressure sensor.
In order to undertake the corresponding repair in a targeted manner in the case of an error in the operation of an internal combustion engine, a method for the diagnosis of the component, especially a rail pressure sensor, of an internal combustion engine is proposed in DE 100 40 254 B4 in which a component which can be the direct cause of an error—combustion outliers are exclusively cited—is checked by the internal combustion engine being explicitly put into a checking state in which the component cannot be the indirect cause of the error which has occurred and a check is then made as to whether the same error is occurring. In detail the explicit switching-off of the rail pressure sensor contained in a closed-loop control path is discussed, with the pressure control valve being controlled after switching off such that the pressure in the rail assumes a so-called default pressure. As an alternative to introducing the test operating state by switching off the component, in the cited patent document it is also mentioned that the component, for example a sensor, can be explicitly replaced by a model valid in specific operating states. It is proposed in particular that the signal delivered by a sensor be computed from the signals of other sensors and that the test mode of the internal combustion engine be based on these computed variables.